Exploring the Ancient Science: How the Greeks Knew That the Earth Is Spherical
Summary
TLDRThis video explores how ancient Greeks deduced the Earth's spherical shape. Around 500 BC, while most believed in a flat Earth, Pythagoras and his students proposed it was spherical. Anaxagoras supported this by observing lunar eclipses. Aristotle provided several arguments, including the varying position of the North Star and the disappearance of ships at sea, suggesting a curved surface. Eratosthenes, using observations of shadows at different locations during the summer solstice, calculated the Earth's circumference to be approximately 40,000 kilometers, offering compelling evidence for a spherical Earth.
Takeaways
- 🌐 The ancient Greeks, notably Pythagoras and his pupils, were among the first to propose that the Earth is spherical, contrary to the common flat Earth belief around 500 BC.
- 🌑 Anaxagoras supported the spherical Earth theory by observing the Earth's shadow on the Moon during lunar eclipses between 500 to 430 BC.
- 📚 Aristotle provided several arguments for a spherical Earth around 340 BC, including the varying positions of the North Star when observed from different locations.
- 🚢 Aristotle also noted that ships disappear hull-first over the horizon, suggesting a curved surface rather than a flat Earth.
- 🌕 He reasoned that if the Moon and the Sun are spherical, it's likely that the Earth is too, based on the uniformity of natural bodies.
- 🔍 Eratosthenes, working at the Library of Alexandria, provided the most accurate measurement of the Earth's size and circumference for his time.
- 📏 Eratosthenes used the difference in shadows at noon in two different locations to calculate the Earth's curvature and circumference.
- 🌞 He hypothesized that the Sun's rays are parallel and used this to determine the angle of the Sun's rays at different locations.
- 📐 From his measurements, Eratosthenes computed the Earth's circumference to be approximately 250,000 stadia, which is about 40,000 kilometers.
- 🧠 The video concludes by challenging viewers to answer a comprehension test based on the information provided about the Greeks' understanding of a spherical Earth.
Q & A
Who were the first Greeks to propose that the Earth is spherical?
-Pythagoras and his pupils were the first to propose that the Earth is spherical.
How did Anaxagoras support Pythagoras's proposal of a spherical Earth?
-Anaxagoras supported Pythagoras's proposal by observing the shadows that the Earth cast on the moon during a lunar eclipse.
What was one of Aristotle's arguments for a spherical Earth?
-One of Aristotle's arguments was the observation that the North Star appears closer to the horizon when the Greeks traveled to places near the equator, like Egypt.
What did Aristotle infer from the observation of ships disappearing over the horizon?
-Aristotle inferred that if the Earth were flat, a ship would become smaller and smaller until it disappeared, but instead, the hull disappeared first, suggesting that the Earth is curved.
How did ancient scholars attempt to calculate the circumference of the Earth?
-Ancient scholars like Eratosthenes attempted to calculate the Earth's circumference through observations and mathematical calculations.
What was the significance of the difference in shadows observed by Eratosthenes between Alexandria and Syene?
-The difference in shadows observed by Eratosthenes indicated that the Sun was not directly overhead in Alexandria during the summer solstice, suggesting that the Earth is curved.
What was the unit of measurement Eratosthenes used to estimate the Earth's circumference?
-Eratosthenes used 'stadia' as the unit of measurement to estimate the Earth's circumference.
What was the approximate circumference of the Earth calculated by Eratosthenes?
-Eratosthenes computed the circumference of the Earth to be approximately 250,000 stadia, which is about 40,000 kilometers.
What was the common belief about the Earth's shape among Greeks around 500 BC?
-Around 500 BC, most Greeks believed that the Earth was flat.
What was the significance of the observation that the North Star's position changes with location?
-The observation that the North Star's position changes with location, being higher in the sky in northern regions and closer to the horizon near the equator, was evidence for the Earth's sphericity.
How did the Greeks' understanding of the Earth's shape evolve from a flat Earth to a spherical Earth?
-The Greeks' understanding evolved through observations like lunar eclipses, the changing position of the North Star, and the disappearance of ships over the horizon, leading to philosophical and scientific arguments supporting a spherical Earth.
Outlines
🌐 Understanding Earth's Sphericity in Ancient Greece
This video explores how ancient Greeks deduced that the Earth is spherical. Initially, around 500 BC, the common belief was that the Earth was flat. However, Pythagoras and his students were the first to suggest a spherical Earth. Anaxagoras later supported this idea by observing the Earth's shadow on the Moon during lunar eclipses. Aristotle, around 340 BC, provided several arguments for a spherical Earth, including the varying positions of the North Star at different latitudes and the observation that ships disappear hull-first over the horizon. Eratosthenes, working at the Library of Alexandria, calculated the Earth's circumference by comparing the shadows cast by the sun at different locations on the summer solstice, leading to a remarkably accurate estimation for his time.
Mindmap
Keywords
💡Spherical Earth
💡Pythagoras
💡Anaxagoras
💡Aristotle
💡North Star
💡Lunar Eclipse
💡Eratosthenes
💡Circumference
💡Stadia
💡Ship Disappearance
💡Parallel Light Rays
Highlights
Around 500 BC, most Greeks believed the Earth was flat.
Pythagoras and his pupils were the first to propose a spherical Earth.
Anaxagoras supported the spherical Earth theory by observing lunar eclipses.
Aristotle provided several arguments for a spherical Earth around 340 BC.
The position of the North Star was an argument for a spherical Earth.
Aristotle also argued that if the moon and sun were spherical, Earth might be too.
The disappearance of ships at sea was another argument for a spherical Earth.
Ancient scholars attempted to calculate the Earth's circumference.
Eratosthenes provided the most accurate measurement of the Earth's size during his time.
Eratosthenes used the angle of the sun's rays at different locations to calculate the Earth's curvature.
He computed the Earth's circumference to be approximately 250,000 stadia.
The stadia was a unit of measurement used to describe a typical stadium at that time.
Eratosthenes' measurement is about 40,000 kilometers, which is remarkably close to the actual value.
The Greeks' understanding of the Earth's shape was based on a combination of observations and logical reasoning.
The video concludes with an eight-item test to check comprehension.
Answers to the test will be provided in the video description.
Transcripts
in this video we are going to talk about
how the Greeks knew that the Earth is
spherical at the end of the lesson you
will be able to explain how the Greeks
knew that the Earth is spherical so
around 500 BC
most Greeks believe that the Earth was
flat okay
but it was fittagoras and his pupils who
were the first to propose a spherical
Earth
and then n500 to 430 BC
anaxagoras supported Pythagoras's
proposal by observing the Shadows that
the Earth cast on the moon during a
lunar eclipse
so around 340 BC
Aristotle again listed several Arguments
for a spherical Earth one of his
arguments was about the position of the
North Star
okay so the North Star was believed to
be at a fixed position in the sky
but when the Greeks traveled to places
near the equator like Egypt
they noticed that the North Star is
closer to the horizon
okay
Aristotle also argued that if the moon
and the sun were both spherical
then perhaps the Earth was also
spherical and if the Earth were flat
then a ship traveling away from an
observer should become smaller and
smaller until it disappeared
but the Greeks observed that the ship
become smaller
and then its Hull disappeared first
before the sale as if it was peeing
enveloped by the water until it
completely disappeared
so these are the arguments made by
Aristotle now let's talk about the size
of the spherical Earth
ancient Scholars tried to provide the
proof of a spherical earth and its
circumference through calculations it
was eratosthenius who gave the most
accurate size during their time
so while he was working at the Library
of Alexandria in third in Egypt
he received correspondence from cyan in
certain Egypt
which stated that a vertical object did
not cast any Shadow at noon time during
summer solstice
but this was not the case in Alexandria
where at noon during the summer solstice
a vertical object still casts a shadow
so these observations could only mean
that the Sun during this time in
Alexandria was not directly overhead
then determine the angle the sun made
with a vertical Direction by measuring
the shadow that a vertical stick casts
he found out that in Alexandria the sun
makes an angle of 7.2 degrees from the
vertical while zero degrees in cyan to
explain the difference he hypothesized
that the light rays coming from the Sun
are parallel and the Earth is curved so
from his measurements he computed the
circumference of the earth to be
approximately 250
000 stadia stadia means a stadium okay
it's a unit of measurement used to
describe a typical Stadium at that time
so this is about 40 000 kilometers now
okay so those are the reasons or things
that made the Greeks believe that the
Earth is spherical
okay so again before we end this video I
want you to answer this eight item test
just the tester comprehension
again the answer will be posted in the
description box
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